The term "profile" as used herein and as used throughout most part of the world, refers to a metal structural shape, i.e. a steel-beam girder or like structural members having at least a pair of spaced apart flanges bridged by a web.
The term "composite profile" is intended to refer to such a structural shape, the open chamber or channel of which, between the flanges, is filled or at least partly filled with another material, generally concrete, the concrete body being secured to the profile to form a composite structural element.
Structural elements of this type may be fabricated so that the outer surfaces of the flanges remain anchored by the concrete. Structural elements of this type have been used successfully as posts, columns and like supporting elements in structures such as dwellings, factories, exposition halls, stadia, warehouses and like structures where fire resistance is an important factor.
In the past such structural elements have been designed based upon the calculation of the static load at room temperature to establish the steel cross section for the profiles contained within the elements and these profiles were then filled with concrete and coated with concrete. The fabrication of such fire-resistant composite structures was expensive and not always satisfactory, since for many purposes it was desirable that the flanges be exposed at least along their outer surfaces for attachment or other purposes.
Thus in U.S. Pat. No. 4,196,558 a composite structural element is described which has its outer flange surfaces free from a concrete coating, i.e. outside the outline of the profile there is no concrete. The concrete is cast between the flanges into the chamber or channel formed between the flanges and in part by the web of the structural shape, and since the concrete is cast in this chamber, it can be referred to as chamber concrete. The chamber concrete is form-fittingly and force-fittingly engaged with elements projecting into the channel or chamber from the steel structural shape to bond the chamber concrete to the steel both at room temperature and under fire conditions.
The steel profile cross section, the concrete cross section and the effective section of the reinforcing steel embedded in the concrete steel all depend on the load-carrying capabilities and the temperature resistance properties desired.
One of the drawbacks of such structural elements, however, is that the exposed flanges are subject to the thermal action of the fire to a pronounced degree and lose strength. This loss of strength of the flanges, which make up the greater part of the cross section of the steel structural shape, significantly weakens the structural element.
In Luxembourg patent document LU 84 772 corresponding to the commonly assigned copending application Ser. No. 603,509 filed Apr. 24, 1984, and referring to German patent document 28 29 864 (see also U.S. Pat. No. 4,196,558), there is recognized the difficulty of ensuring the requisite temperature distribution in the body of the structural element solely by use of the reinforcing members and there is proposed the embedding in the concrete of at least one further profile or steel structural shape which is connected to the web of the main profile whose outer flange surfaces are not coated with concrete.
Since a portion of this auxiliary or additional profile or structural shape is thermally protected by the surrounding body of concrete, the post, column or girder has especially high load-carrying capacity even under extreme thermal stress as in the case of a fire.
While this structural element has been found to be highly successful in some applications because of its comparatively high cost, large dimensions, complicated construction and mass, it is not useful in many applications although it continues to be a structural element of choice in high-rise construction.